Network Working Group P. Quinn, Ed.
Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track U. Elzur, Ed.
Expires: September 25, 2015 Intel
March 24, 2015
Network Service Header
draft-ietf-sfc-nsh-00.txt
Abstract
This draft describes a Network Service Header (NSH) inserted onto
encapsulated packets or frames to realize service function paths.
NSH also provides a mechanism for metadata exchange along the
instantiated service path.
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1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on September 25, 2015.
Copyright Notice
Copyright (c) 2015 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents
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publication of this document. Please review these documents
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to this document. Code Components extracted from this document must
include Simplified BSD License text as described in Section 4.e of
the Trust Legal Provisions and are provided without warranty as
described in the Simplified BSD License.
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Table of Contents
1. Requirements Language . . . . . . . . . . . . . . . . . . . . 2
2. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2.1. Definition of Terms . . . . . . . . . . . . . . . . . . . 4
2.2. Problem Space . . . . . . . . . . . . . . . . . . . . . . 6
3. Network Service Header . . . . . . . . . . . . . . . . . . . . 8
3.1. Network Service Header Format . . . . . . . . . . . . . . 8
3.2. NSH Base Header . . . . . . . . . . . . . . . . . . . . . 8
3.3. Service Path Header . . . . . . . . . . . . . . . . . . . 10
3.4. NSH MD-type 1 . . . . . . . . . . . . . . . . . . . . . . 10
3.4.1. Mandatory Context Header Allocation Guidelines . . . . 11
3.5. NSH MD-type 2 . . . . . . . . . . . . . . . . . . . . . . 12
3.5.1. Optional Variable Length Metadata . . . . . . . . . . 13
4. NSH Actions . . . . . . . . . . . . . . . . . . . . . . . . . 15
5. NSH Encapsulation . . . . . . . . . . . . . . . . . . . . . . 17
6. NSH Usage . . . . . . . . . . . . . . . . . . . . . . . . . . 18
7. NSH Proxy Nodes . . . . . . . . . . . . . . . . . . . . . . . 19
8. Fragmentation Considerations . . . . . . . . . . . . . . . . . 20
9. Service Path Forwarding with NSH . . . . . . . . . . . . . . . 21
9.1. SFFs and Overlay Selection . . . . . . . . . . . . . . . . 21
9.2. Mapping NSH to Network Overlay . . . . . . . . . . . . . . 23
9.3. Service Plane Visibility . . . . . . . . . . . . . . . . . 24
9.4. Service Graphs . . . . . . . . . . . . . . . . . . . . . . 24
10. Policy Enforcement with NSH . . . . . . . . . . . . . . . . . 26
10.1. NSH Metadata and Policy Enforcement . . . . . . . . . . . 26
10.2. Updating/Augmenting Metadata . . . . . . . . . . . . . . . 27
10.3. Service Path ID and Metadata . . . . . . . . . . . . . . . 29
11. NSH Encapsulation Examples . . . . . . . . . . . . . . . . . . 30
11.1. GRE + NSH . . . . . . . . . . . . . . . . . . . . . . . . 30
11.2. VXLAN-gpe + NSH . . . . . . . . . . . . . . . . . . . . . 30
11.3. Ethernet + NSH . . . . . . . . . . . . . . . . . . . . . . 31
12. Security Considerations . . . . . . . . . . . . . . . . . . . 32
13. Open Items for WG Discussion . . . . . . . . . . . . . . . . . 33
14. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 34
15. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 37
16. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 38
16.1. NSH EtherType . . . . . . . . . . . . . . . . . . . . . . 38
16.2. Network Service Header (NSH) Parameters . . . . . . . . . 38
16.2.1. NSH Base Header Reserved Bits . . . . . . . . . . . . 38
16.2.2. MD Type Registry . . . . . . . . . . . . . . . . . . . 38
16.2.3. TLV Class Registry . . . . . . . . . . . . . . . . . . 39
16.2.4. NSH Base Header Next Protocol . . . . . . . . . . . . 39
17. References . . . . . . . . . . . . . . . . . . . . . . . . . . 40
17.1. Normative References . . . . . . . . . . . . . . . . . . . 40
17.2. Informative References . . . . . . . . . . . . . . . . . . 40
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 42
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2. Introduction
Service functions are widely deployed and essential in many networks.
These service functions provide a range of features such as security,
WAN acceleration, and server load balancing. Service functions may
be instantiated at different points in the network infrastructure
such as the wide area network, data center, campus, and so forth.
The current service function deployment models are relatively static,
and bound to topology for insertion and policy selection.
Furthermore, they do not adapt well to elastic service environments
enabled by virtualization.
New data center network and cloud architectures require more flexible
service function deployment models. Additionally, the transition to
virtual platforms requires an agile service insertion model that
supports elastic service delivery; the movement of service functions
and application workloads in the network and the ability to easily
bind service policy to granular information such as per-subscriber
state are necessary.
The approach taken by NSH is composed of the following elements:
1. Service path identification
2. Transport independent per-packet/frame service metadata.
3. Optional variable TLV metadata.
NSH is designed to be easy to implement across a range of devices,
both physical and virtual, including hardware platforms.
An NSH aware control plane is outside the scope of this document.
The SFC Architecture document [SFC-arch] provides an overview of a
service chaining architecture that clearly defines the roles of the
various elements and the scope of a service function chaining
encapsulation.
2.1. Definition of Terms
Classification: Locally instantiated policy and customer/network/
service profile matching of traffic flows for identification of
appropriate outbound forwarding actions.
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SFC Network Forwarder (NF): SFC network forwarders provide network
connectivity for service functions forwarders and service
functions. SFC network forwarders participate in the network
overlay used for service function chaining as well as in the SFC
encapsulation.
Service Function Forwarder (SFF): A service function forwarder is
responsible for delivering traffic received from the NF to one or
more connected service functions, and from service functions to
the NF.
Service Function (SF): A function that is responsible for specific
treatment of received packets. A service function can act at the
network layer or other OSI layers. A service function can be a
virtual instance or be embedded in a physical network element.
One of multiple service functions can be embedded in the same
network element. Multiple instances of the service function can
be enabled in the same administrative domain.
Service Node (SN): Physical or virtual element that hosts one or
more service functions and has one or more network locators
associated with it for reachability and service delivery.
Service Function Chain (SFC): A service function chain defines an
ordered set of service functions that must be applied to packets
and/or frames selected as a result of classification. The implied
order may not be a linear progression as the architecture allows
for nodes that copy to more than one branch. The term service
chain is often used as shorthand for service function chain.
Service Function Path (SFP): The instantiation of a SFC in the
network. Packets follow a service function path from a classifier
through the requisite service functions
Network Node/Element: Device that forwards packets or frames based
on outer header information. In most cases is not aware of the
presence of NSH.
Network Overlay: Logical network built on top of existing network
(the underlay). Packets are encapsulated or tunneled to create
the overlay network topology.
Network Service Header: Data plane header added to frames/packets.
The header contains information required for service chaining, as
well as metadata added and consumed by network nodes and service
elements.
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Service Classifier: Function that performs classification and
imposes an NSH. Creates a service path. Non-initial (i.e.
subsequent) classification can occur as needed and can alter, or
create a new service path.
Service Hop: NSH aware node, akin to an IP hop but in the service
overlay.
Service Path Segment: A segment of a service path overlay.
NSH Proxy: Acts as a gateway: removes and inserts NSH on behalf of a
service function that is not NSH aware.
2.2. Problem Space
Network Service Header (NSH) addresses several limitations associated
with service function deployments today.
1. Topological Dependencies: Network service deployments are often
coupled to network topology. Such dependency imposes constraints
on the service delivery, potentially inhibiting the network
operator from optimally utilizing service resources, and reduces
the flexibility. This limits scale, capacity, and redundancy
across network resources.
2. Service Chain Construction: Service function chains today are
most typically built through manual configuration processes.
These are slow and error prone. With the advent of newer service
deployment models the control/management planes provide not only
connectivity state, but will also be increasingly utilized for
the creation of network services. Such a control/management
planes could be centralized, or be distributed.
3. Application of Service Policy: Service functions rely on topology
information such as VLANs or packet (re) classification to
determine service policy selection, i.e. the service function
specific action taken. Topology information is increasingly less
viable due to scaling, tenancy and complexity reasons. The
topological information is often stale, providing the operator
with inaccurate placement that can result in suboptimal resource
utilization. Furthermore topology-centric information often does
not convey adequate information to the service functions, forcing
functions to individually perform more granular classification.
4. Per-Service (re)Classification: Classification occurs at each
service function independent from previously applied service
functions. More importantly, the classification functionality
often differs per service function and service functions may not
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leverage the results from other service functions.
5. Common Header Format: Various proprietary methods are used to
share metadata and create service paths. An open header provides
a common format for all network and service devices.
6. Limited End-to-End Service Visibility: Troubleshooting service
related issues is a complex process that involve both network-
specific and service-specific expertise. This is especially the
case when service function chains span multiple DCs, or across
administrative boundaries. Furthermore, the physical and virtual
environments (network and service) can be highly divergent in
terms of topology and that topological variance adds to these
challenges.
7. Transport Dependence: Service functions can and will be deployed
in networks with a range of transports requiring service
functions to support and participate in many transports (and
associated control planes) or for a transport gateway function to
be present.
Please see the Service Function Chaining Problem Statement [SFC-PS]
for a more detailed analysis of service function deployment problem
areas.
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3. Network Service Header
A Network Service Header (NSH) contains metadata and service path
information that are added to a packet or frame and used to create a
service plane. The packets and the NSH are then encapsulated in an
outer header for transport.
The service header is added by a service classification function - a
device or application - that determines which packets require
servicing, and correspondingly which service path to follow to apply
the appropriate service.
3.1. Network Service Header Format
An NSH is composed of a 4-byte base header, a 4-byte service path
header and context headers, as shown in Figure 1 below.
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Base Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Service Path Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Context Headers ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Network Service Header
Base header: provides information about the service header and the
payload protocol.
Service Path Header: provide path identification and location within
a path.
Context headers: carry opaque metadata and variable length encoded
information.
3.2. NSH Base Header
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Ver|O|C|R|R|R|R|R|R| Length | MD Type | Next Protocol |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Figure 2: NSH Base Header
Base Header Field Descriptions
Version: The version field is used to ensure backward compatibility
going forward with future NSH updates.
O bit: Indicates that this packet is an operations and management
(OAM) packet. SFF and SFs nodes MUST examine the payload and take
appropriate action (e.g. return status information).
OAM message specifics and handling details are outside the scope of
this document.
C bit: Indicates that a critical metadata TLV is present (see Section
3.4.2). This bit acts as an indication for hardware implementers to
decide how to handle the presence of a critical TLV without
necessarily needing to parse all TLVs present. The C bit MUST be set
to 1 if one or more critical TLVs are present.
All other flag fields are reserved.
Length: total length, in 4-byte words, of the NSH header, including
optional variable TLVs.
MD Type: indicates the format of NSH beyond the base header and the
type of metadata being carried. This typing is used to describe the
use for the metadata. A new registry will be requested from IANA for
the MD Type.
NSH defines two MD types:
0x1 which indicates that the format of the header includes fixed
length context headers.
0x2 which does not mandate any headers beyond the base header and
service path header, and may contain optional variable length context
information.
The format of the base header is invariant, and not described by MD
Type.
NSH implementations MUST support MD-Type 0x1, and SHOULD support MD-
Type 0x2.
Next Protocol: indicates the protocol type of the original packet. A
new IANA registry will be created for protocol type.
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This draft defines the following Next Protocol values:
0x1 : IPv4
0x2 : IPv6
0x3 : Ethernet
3.3. Service Path Header
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Service Path ID | Service Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Service path ID (SPI): 24 bits
Service index (SI): 8 bits
Figure 3: NSH Service Path Header
Service Path Identifier (SPI): identifies a service path.
Participating nodes MUST use this identifier for path selection. An
administrator can use the service path value for reporting and
troubleshooting packets along a specific path.
Service Index (SI): provides location within the service path.
Service index MUST be decremented by service functions or proxy nodes
after performing required services. MAY be used in conjunction with
service path for path selection. Service Index is also valuable when
troubleshooting/reporting service paths. In addition to location
within a path, SI can be used for loop detection.
3.4. NSH MD-type 1
When the base header specifies MD Type 1, NSH defines four 4-byte
mandatory context headers, as per Figure 4. These headers must be
present and the format is opaque as depicted in Figure 5.
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0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Ver|O|C|R|R|R|R|R|R| Length | MD-type=0x1 | Next Protocol |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Service Path ID | Service Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mandatory Context Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mandatory Context Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mandatory Context Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Mandatory Context Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: NSH MD-type=0x1
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Context data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Context Header
3.4.1. Mandatory Context Header Allocation Guidelines
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Platform Context |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Network Shared Context |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Service Platform Context |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Service Shared Context |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Figure 6: Context Data Significance
Figure 6, above, and the following examples of context header
allocation are guidelines that illustrate how various forms of
information can be carried and exchanged via NSH.
Network platform context: provides platform-specific metadata shared
between network nodes. Examples include (but are not limited to)
ingress port information, forwarding context and encapsulation type.
Network shared context: metadata relevant to any network node such as
the result of edge classification. For example, application
information, identity information or tenancy information can be
shared using this context header.
Service platform context: provides service platform specific metadata
shared between service functions. This context header is analogous
to the network platform context, enabling service platforms to
exchange platform-centric information such as an identifier used for
load balancing decisions.
Service shared context: metadata relevant to, and shared, between
service functions. As with the shared network context,
classification information such as application type can be conveyed
using this context.
The data center[dcalloc] and mobility[moballoc] context header
allocation drafts provide guidelines for the semantics of NSH fixed
context headers in each respective environment.
3.5. NSH MD-type 2
When the base header specifies MD Type 2, NSH defines variable length
only context headers. There may be zero or more of these headers as
per the length field.
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Ver|O|C|R|R|R|R|R|R| Length | MD-type=0x2 | Next Protocol |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Service Path ID | Service Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
~ Optional Variable Length Context Headers ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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Figure 7: NSH MD-type=0x2
3.5.1. Optional Variable Length Metadata
NSH MD Type 2 MAY contain optional variable length context headers.
The format of these headers is as described below.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TLV Class | Type |R|R|R| Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Variable Metadata |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: Variable Context Headers
TLV Class: describes the scope of the "Type" field. In some cases,
the TLV Class will identify a specific vendor, in others, the TLV
Class will identify specific standards body allocated types.
Type: the specific type of information being carried, within the
scope of a given TLV Class. Value allocation is the responsibility
of the TLV Class owner.
The most significant bit of the Type field indicates whether the TLV
is mandatory for the receiver to understand/process. This
effectively allocates Type values 0 to 127 for non-critical options
and Type values 128 to 255 for critical options. Figure 7 below
illustrates the placement of the Critical bit within the Type field.
+-+-+-+-+-+-+-+-+
|C| Type |
+-+-+-+-+-+-+-+-+
Figure 9: Critical Bit Placement Within the TLV Type Field
Encoding the criticality of the TLV within the Type field is
consistent with IPv6 option types.
If a receiver receives an encapsulated packet containing a TLV with
the Critical bit set in the Type field and it does not understand how
to process the Type, it MUST drop the packet. Transit devices MUST
NOT drop packets based on the setting of this bit.
Reserved bits: three reserved bit are present for future use. The
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reserved bits MUST be zero.
Length: Length of the variable metadata, in 4-byte words.
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4. NSH Actions
Service header aware nodes - service classifiers, SFF, SF and NSH
proxies, have several possible header related actions:
1. Insert or remove service header: These actions can occur at the
start and end respectively of a service path. Packets are
classified, and if determined to require servicing, a service
header imposed. The last node in a service path, an SFF, removes
the NSH. A service classifier MUST insert an NSH. At the end of
a service function chain, the last node operating on the service
header MUST remove it.
A service function can re-classify data as required and that re-
classification might result in a new service path. In this case,
the SF acts as a logical classifier as well. When the logical
classifier performs re-classification that results in a change of
service path, it MUST remove the existing NSH and MUST impose a
new NSH with the base header reflecting the new path.
2. Select service path: The base header provides service chain
information and is used by SFFs to determine correct service path
selection. SFFs MUST use the base header for selecting the next
service in the service path.
3. Update a service header: NSH aware service functions MUST
decrement the service index. A service index = 0 indicates that
a packet MUST be dropped by the SFF performing NSH-based
forwarding.
Service functions MAY update context headers if new/updated
context is available.
If an NSH proxy (see Section 7) is in use (acting on behalf of a
non-NSH-aware service function for NSH actions), then the proxy
MUST update service index and MAY update contexts. When an NSH
proxy receives an NSH-encapsulated packet, it removes the NSH
before forwarding it to an NSH unaware SF. When it receives a
packet back from an NSH unaware SF, it re-encapsulates it with
the NSH, decrementing the service index.
4. Service policy selection: Service function instances derive
policy selection from the service header. Context shared in the
service header can provide a range of service-relevant
information such as traffic classification. Service functions
SHOULD use NSH to select local service policy.
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Figure 10 maps each of the four actions above to the components in
the SFC architecture that can perform it.
+----------------+--------------------+-------+---------------+-------+
| | Insert or remove |Select | Update a |Service|
| | service header |service|service header |Policy |
| +------+------+------+ path +---------------+Select-|
| |Insert|Remove|Remove| | Dec. |Update |ion |
| | | | and | |Service|Context| |
| Component | | |Insert| | Index |Header | |
+----------------+------+------+------+-------+-------+-------+-------+
|Service Classif-| + | | | | | + | |
|ication Function| | | | | | | |
+ -------------- + ---- + ---- + ---- + ----- + ----- + ----- + ----- +
|Service Function| | + | | + | | + | |
|Forwarder(SFF) | | | | | | | |
+ -------------- + ---- + ---- + ---- + ----- + ----- + ----- + ----- +
|Service | | | | | + | + | + |
|Function (SF) | | | | | | | |
+ -------------- + ---- + ---- + ---- + ----- + ----- + ----- + ----- +
|NSH Proxy | + | + | | | + | + | |
+----------------+------+------+------+-------+-------+-------+-------+
Figure 10: NSH Action and Role Mapping
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5. NSH Encapsulation
Once NSH is added to a packet, an outer encapsulation is used to
forward the original packet and the associated metadata to the start
of a service chain. The encapsulation serves two purposes:
1. Creates a topologically independent services plane. Packets are
forwarded to the required services without changing the
underlying network topology.
2. Transit network nodes simply forward the encapsulated packets as
is.
The service header is independent of the encapsulation used and is
encapsulated in existing transports. The presence of NSH is
indicated via protocol type or other indicator in the outer
encapsulation.
See Section 11 for NSH encapsulation examples.
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6. NSH Usage
The NSH creates a dedicated service plane, that addresses many of the
limitations highlighted in Section 2.2. More specifically, NSH
enables:
1. Topological Independence: Service forwarding occurs within the
service plane, via a network overlay, the underlying network
topology does not require modification. Service functions have
one or more network locators (e.g. IP address) to receive/send
data within the service plane, the NSH contains an identifier
that is used to uniquely identify a service path and the services
within that path.
2. Service Chaining: NSH contains path identification information
needed to realize a service path. Furthermore, NSH provides the
ability to monitor and troubleshoot a service chain, end-to-end
via service-specific OAM messages. The NSH fields can be used by
administrators (via, for example a traffic analyzer) to verify
(account, ensure correct chaining, provide reports, etc.) the
path specifics of packets being forwarded along a service path.
3. Metadata Sharing: NSH provides a mechanism to carry shared
metadata between network devices and service function, and
between service functions. The semantics of the shared metadata
is communicated via a control plane to participating nodes.
Examples of metadata include classification information used for
policy enforcement and network context for forwarding post
service delivery.
4. Transport Agnostic: NSH is transport independent and is carried
in an overlay, over existing underlays. If an existing overlay
topology provides the required service path connectivity, that
existing overlay may be used.
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7. NSH Proxy Nodes
In order to support NSH-unaware service functions, an NSH proxy is
used. The proxy node removes the NSH header and delivers the
original packet/frame via a local attachment circuit to the service
function. Examples of a local attachment circuit include, but are
not limited to: VLANs, IP in IP, GRE, VXLAN. When complete, the
service function returns the packet to the NSH proxy via the same or
different attachment circuit.
NSH is re-imposed on packets returned to the proxy from the non-NSH-
aware service.
Typically, an SFF will act as an NSH-proxy when required.
An NSH proxy MUST perform NSH actions as described in Section 4.
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8. Fragmentation Considerations
Work in progress
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9. Service Path Forwarding with NSH
9.1. SFFs and Overlay Selection
As described above, NSH contains a service path identifier (SPI) and
a service index (SI). The SPI is, as per its name, an identifier.
The SPI alone cannot be used to forward packets along a service path.
Rather the SPI provide a level of indirection between the service
path/topology and the network transport. Furthermore, there is no
requirement, or expectation of an SPI being bound to a pre-determined
or static network path.
The service index provides an indication of location within a service
path. The combination of SPI and SI provides the identification and
location of a logical SF (locator and order). The logical SF may be
a single SF, or a set of SFs that are equivalent. In the latter
case, the SFF provides load distribution amongst the collection of
SFs as needed. SI may also serve as a mechanism for loop detection
with in a service path since each SF in the path decrements the
index; an index of 0 indicates that a loop occurred and packet must
be discarded.
This indirection -- path ID to overlay -- creates a true service
plane. That is the SFF/SF topology is constructed without impacting
the network topology but more importantly service plane only
participants (i.e. most SFs) need not be part of the network overlay
topology and its associated infrastructure (e.g. control plane,
routing tables, etc.). As mentioned above, an existing overlay
topology may be used provided it offers the requisite connectivity.
The mapping of SPI to transport occurs on an SFF. The SFF consults
the SPI/ID values to determine the appropriate overlay transport
protocol (several may be used within a given network) and next hop
for the requisite SF. Figure 10 below depicts an SPI/SI to network
overlay mapping.
+-------------------------------------------------------+
| SPI | SI | NH | Transport |
+-------------------------------------------------------+
| 10 | 3 | 1.1.1.1 | VXLAN-gpe |
| 10 | 2 | 2.2.2.2 | nvGRE |
| 245 | 12 | 192.168.45.3 | VXLAN-gpe |
| 10 | 9 | 10.1.2.3 | GRE |
| 40 | 9 | 10.1.2.3 | GRE |
| 50 | 7 | 01:23:45:67:89:ab | Ethernet |
| 15 | 1 | Null (end of path) | None |
+-------------------------------------------------------+
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Figure 11: SFF NSH Mapping Example
Additionally, further indirection is possible: the resolution of the
required SF function locator may be a localized resolution on an
SFF,rather than a service function chain control plane
responsibility, as per figures 11 and 12 below.
+-------------------+
| SPI | SI | NH |
+-------------------+
| 10 | 3 | SF2 |
| 245 | 12 | SF34 |
| 40 | 9 | SF9 |
+-------------------+
Figure 12: NSH to SF Mapping Example
+-----------------------------------+
| SF | NH | Transport |
+-----------------------------------|
| SF2 | 10.1.1.1 | VXLAN-gpe |
| SF34| 192.168.1.1 | UDP |
| SF9 | 1.1.1.1 | GRE |
+-----------------------------------+
Figure 13: SF Locator Mapping Example
Since the SPI is a representation of the service path, the lookup may
return more than one possible next-hop within a service path for a
given SF, essentially a series of weighted (equally or otherwise)
overlay links to be used (for load distribution, redundancy or
policy), see Figure 13. The metric depicted in Figure 13 is an
example to help illustrated weighing SFs. In a real network, the
metric will range from a simple preference (similar to routing next-
hop), to a true dynamic composite metric based on some service
function-centric state (including load, sessions sate, capacity,
etc.)
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+----------------------------------+
| SPI | SI | NH | Metric |
+----------------------------------+
| 10 | 3 | 10.1.1.1 | 1 |
| | | 10.1.1.2 | 1 |
| | | | |
| 20 | 12 | 192.168.1.1 | 1 |
| | | 10.2.2.2 | 1 |
| | | | |
| 30 | 7 | 10.2.2.3 | 10 |
| | | 10.3.3.3 | 5 |
+----------------------------------+
(encap type omitted for formatting)
Figure 14: NSH Weighted Service Path
9.2. Mapping NSH to Network Overlay
As described above, the mapping of SPI to network topology may result
in a single overlay path, or it might result in a more complex
topology. Furthermore, the SPIx to overlay mapping occurs at each
SFF independently. Any combination of topology selection is
possible.
Examples of mapping for a topology:
1. Next SF is located at SFFb with locator 10.1.1.1
SFFa mapping: SPI=10 --> VXLAN-gpe, dst-ip: 10.1.1.1
2. Next SF is located at SFFc with multiple locator for load
distribution purposes:
SFFb mapping: SPI=10 --> VXLAN-gpe, dst_ip:10.2.2.1, 10.2.2.2,
10.2.2.3, equal cost
3. Next SF is located at SFFd with two path to SFFc, one for
redundancy:
SFFc mapping: SPI=10 --> VXLAN-gpe, dst_ip:10.1.1.1 cost=10,
10.1.1.2, cost=20
In the above example, each SFF makes an independent decision about
the network overlay path and policy for that path. In other words,
there is no a priori mandate about how to forward packets in the
network (only the order of services that must be traversed).
The network operator retains the ability to engineer the overlay
paths as required. For example, the overlay path between service
functions forwarders may utilize traffic engineering, QoS marking, or
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ECMP, without requiring complex configuration and network protocol
support to be extended to the service path explicitly. In other
words, the network operates as expected, and evolves as required, as
does the service function plane.
9.3. Service Plane Visibility
The SPI and SI serve an important function for visibility into the
service topology. An operator can determine what service path a
packet is "on", and its location within that path simply by viewing
the NSH information (packet capture, IPFIX, etc.). The information
can be used for service scheduling and placement decisions,
troubleshooting and compliance verification.
9.4. Service Graphs
In some cases, a service path is exactly that -- a linear list of
service functions that must be traversed. However, increasingly, the
"path" is actually a true directed graph. Furthermore, within a
given service topology several directed graphs may exist with packets
moving between graphs based on non-initial classification (usually
performed by a service function). Note: strictly speaking a path is
a form of graph; the intent is to distinguish between a directed
graph and a path.
,---. ,---. ,---.
/ \ / \ / \
( SF2 ) ( SF7 ) ( SF3 )
,------\ +. \ / \ /
; |---' `-. `---'\ `-+-'
| : : \ ;
| \ | : ;
,-+-. `. ,+--. : |
/ \ '---+ \ \ ;
( SF1 ) ( SF6 ) \ /
\ / \ +--. : /
`---' `---' `-. ,-+-. /
`+ +'
( SF4 )
\ /
`---'
Figure 15: Service Graph Example
The SPI/SI combination provides a simple representation of a directed
graph, the SPI represents a graph ID; and the SI a node ID. The
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service topology formed by SPI/SI support cycles, weighting, and
alternate topology selection, all within the service plane. The
realization of the network topology occurs as described above: SPI/ID
mapping to an appropriate transport and associated next network hops.
NSH-aware services receive the entire header, including the SPI/SI.
An SF can now, based on local policy, alter the SPI, which in turn
effects both the service graph, and in turn the selection of overlay
at the SFF. The figure below depicts the policy associated with the
graph in Figure 14 above. Note: this illustrates multiple graphs and
their representation; it does not depict the use of metadata within a
single service function graph.
+---------------------------------------------------------------------+
| SPI: 21 Bob: SF7 |
| SPI: 20 Bad : SF2 --> SF6 --> SF4 |
|SPI: 10 SF1 --> SF2 --> SF6 SPI: 22 Alice: SF3 |
| SPI: 30 Good: SF4 |
| SPI:31 Bob: SF7 |
| SPI:32 Alice: SF3 |
+---------------------------------------------------------------------+
Figure 16: Service Graphs Using SPI
This example above does not show the mapping of the service topology
to the network overlay topology. As discussed in the sections above,
the overlay selection occurs as per network policy.
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10. Policy Enforcement with NSH
10.1. NSH Metadata and Policy Enforcement
As described in Section 3, NSH provides the ability to carry metadata
along a service path. This metadata may be derived from several
sources, common examples include:
Network nodes: Information provided by network nodes can indicate
network-centric information (such as VRF or tenant) that may be
used by service functions, or conveyed to another network node
post-service pathing.
External (to the network) systems: External systems, such as
orchestration systems, often contain information that is valuable
for service function policy decisions. In most cases, this
information cannot be deduced by network nodes. For example, a
cloud orchestration platform placing workloads "knows" what
application is being instantiated and can communicate this
information to all NSH nodes via metadata.
Service functions: Service functions often perform very detailed
and valuable classification. In some cases they may terminate,
and be able to inspect encrypted traffic. SFs may update, alter
or impose metadata information.
Regardless of the source, metadata reflects the "result" of
classification. The granularity of classification may vary. For
example, a network switch might only be able to classify based on a
5-tuple, whereas, a service function may be able to inspect
application information. Regardless of granularity, the
classification information can be represented in NSH.
Once the data is added to NSH, it is carried along the service path,
NSH-aware SFs receive the metadata, and can use that metadata for
local decisions and policy enforcement. The following two examples
highlight the relationship between metadata and policy:
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+-------------------------------------------------+
| ,---. ,---. ,---. |
| / \ / \ / \ |
| ( SCL )-------->( SF1 )--------->( SF2 ) |
| \ / \ / \ / |
| `---' `---' `---' |
|5-tuple: Permit Inspect |
|Tenant A Tenant A AppY |
|AppY |
+-------------------------------------------------+
Figure 17: Metadata and Policy
+-------------------------------------------------+
| ,---. ,---. ,---. |
| / \ / \ / \ |
| ( SCL )-------->( SF1 )--------->( SF2 ) |
| \ / \ / \ / |
| `-+-' `---' `---' |
| | Permit Deny AppZ |
| +---+---+ employees |
| | | |
| +-------+ |
| external |
| system: |
| Employee |
| App Z |
+-------------------------------------------------+
Figure 18: External Metadata and Policy
In both of the examples above, the service functions perform policy
decisions based on the result of the initial classification: the SFs
did not need to perform re-classification, rather they relied on a
antecedent classification for local policy enforcement.
10.2. Updating/Augmenting Metadata
Post-initial metadata imposition (typically performed during initial
service path determination), metadata may be augmented or updated:
1. Metadata Augmentation: Information may be added to NSH's existing
metadata, as depicted in Figure 18. For example, if the initial
classification returns the tenant information, a secondary
classification (perhaps a DPI or SLB) may augment the tenant
classification with application information. The tenant
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classification is still valid and present, but additional
information has been added to it.
2. Metadata Update: Subsequent classifiers may update the initial
classification if it is determined to be incorrect or not
descriptive enough. For example, the initial classifier adds
metadata that describes the trafic as "internet" but a security
service function determines that the traffic is really "attack".
Figure 19 illustrates an example of updating metadata.
+-------------------------------------------------+
| ,---. ,---. ,---. |
| / \ / \ / \ |
| ( SCL )-------->( SF1 )--------->( SF2 ) |
| \ / \ / \ / |
| `-+-' `---' `---' |
| | Inspect Deny |
| +---+---+ employees employee+ |
| | | Class=AppZ appZ |
| +-------+ |
| external |
| system: |
| Employee |
| |
+-------------------------------------------------+
Figure 19: Metadata Augmentation
+-------------------------------------------------+
| ,---. ,---. ,---. |
| / \ / \ / \ |
| ( SCL )-------->( SF1 )--------->( SF2 ) |
| \ / \ / \ / |
| `---' `---' `---' |
|5-tuple: Inspect Deny |
|Tenant A Tenant A attack |
| --> attack |
+-------------------------------------------------+
Figure 20: Metadata Update
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10.3. Service Path ID and Metadata
Metadata information may influence the service path selection since
the service path identifier can represent the result of
classification. A given SPI can represent all or some of the
metadata, and be updated based on metadata classification results.
This relationship provides the ability to create a dynamic services
plane based on complex classification without requiring each node to
be capable of such classification, or requiring a coupling to the
network topology. This yields service graph functionality as
described in Section 9.4. Figure 20 illustrates an example of this
behavior.
+----------------------------------------------------+
| ,---. ,---. ,---. |
| / \ / \ / \ |
| ( SCL )-------->( SF1 )--------->( SF2 ) |
| \ / \ / \ / |
| `---' `---' \ `---' |
|5-tuple: Inspect \ Original |
|Tenant A Tenant A \ next SF |
| --> DoS \ |
| \ |
| ,---. |
| / \ |
| ( SF10 ) |
| \ / |
| `---' |
| DoS |
| "Scrubber" |
+----------------------------------------------------+
Figure 21: Path ID and Metadata
Specific algorithms for mapping metadata to an SPI are outside the
scope of this draft.
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11. NSH Encapsulation Examples
11.1. GRE + NSH
IPv4 Packet:
+----------+--------------------+--------------------+
|L2 header | L3 header, proto=47|GRE header,PT=0x894F|
+----------+--------------------+--------------------+
--------------+----------------+
NSH, NP=0x1 |original packet |
--------------+----------------+
L2 Frame:
+----------+--------------------+--------------------+
|L2 header | L3 header, proto=47|GRE header,PT=0x894F|
+----------+--------------------+--------------------+
---------------+---------------+
NSH, NP=0x3 |original frame |
---------------+---------------+
Figure 22: GRE + NSH
11.2. VXLAN-gpe + NSH
IPv4 Packet:
+----------+------------------------+---------------------+
|L2 header | IP + UDP dst port=4790 |VXLAN-gpe NP=0x4(NSH)|
+----------+------------------------+---------------------+
--------------+----------------+
NSH, NP=0x1 |original packet |
--------------+----------------+
L2 Frame:
+----------+------------------------+---------------------+
|L2 header | IP + UDP dst port=4790 |VXLAN-gpe NP=0x4(NSH)|
+----------+------------------------+---------------------+
---------------+---------------+
NSH,NP=0x3 |original frame |
---------------+---------------+
Figure 23: VXLAN-gpe + NSH
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11.3. Ethernet + NSH
IPv4 Packet:
+-------------------------------+---------------+--------------------+
|Outer Ethernet, ET=0x894F | NSH, NP = 0x1 | original IP Packet |
+-------------------------------+---------------+--------------------+
L2 Frame:
+-------------------------------+---------------+----------------+
|Outer Ethernet, ET=0x894F | NSH, NP = 0x3 | original frame |
+-------------------------------+---------------+----------------+
Figure 24: Ethernet + NSH
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12. Security Considerations
As with many other protocols, NSH data can be spoofed or otherwise
modified. In many deployments, NSH will be used in a controlled
environment, with trusted devices (e.g. a data center) thus
mitigating the risk of unauthorized header manipulation.
NSH is always encapsulated in a transport protocol and therefore,
when required, existing security protocols that provide authenticity
(e.g. RFC 2119 [RFC6071]) can be used.
Similarly if confidentiality is required, existing encryption
protocols can be used in conjunction with encapsulated NSH.
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13. Open Items for WG Discussion
1. MD type 1 metadata semantics specifics
2. Bypass bit in NSH.
3. Rendered Service Path ID (RSPID).
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14. Contributors
This WG document originated as draft-quinn-sfc-nsh and had the
following co-authors and contributors. The editors of this document
would like to thank and recognize them and their contributions.
These co-authors and contributors provided invaluable concepts and
content for this document's creation.
Surendra Kumar
Cisco Systems
smkumar@cisco.com
Michael Smith
Cisco Systems
michsmit@cisco.com
Jim Guichard
Cisco Systems
jguichar@cisco.com
Rex Fernando
Cisco Systems
Email: rex@cisco.com
Navindra Yadav
Cisco Systems
Email: nyadav@cisco.com
Wim Henderickx
Alcatel-Lucent
wim.henderickx@alcatel-lucent.com
Andrew Dolganow
Alcaltel-Lucent
Email: andrew.dolganow@alcatel-lucent.com
Praveen Muley
Alcaltel-Lucent
Email: praveen.muley@alcatel-lucent.com
Tom Nadeau
Brocade
tnadeau@lucidvision.com
Puneet Agarwal
puneet@acm.org
Rajeev Manur
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Broadcom
rmanur@broadcom.com
Abhishek Chauhan
Citrix
Abhishek.Chauhan@citrix.com
Joel Halpern
Ericsson
joel.halpern@ericsson.com
Sumandra Majee
F5
S.Majee@f5.com
David Melman
Marvell
davidme@marvell.com
Pankaj Garg
Microsoft
Garg.Pankaj@microsoft.com
Brad McConnell
Rackspace
bmcconne@rackspace.com
Chris Wright
Red Hat Inc.
chrisw@redhat.com
Kevin Glavin
Riverbed
kevin.glavin@riverbed.com
Hong (Cathy) Zhang
Huawei US R&D
cathy.h.zhang@huawei.com
Louis Fourie
Huawei US R&D
louis.fourie@huawei.com
Ron Parker
Affirmed Networks
ron_parker@affirmednetworks.com
Myo Zarny
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Goldman Sachs
myo.zarny@gs.com
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15. Acknowledgments
The authors would like to thank Nagaraj Bagepalli, Abhijit Patra,
Peter Bosch, Darrel Lewis, Pritesh Kothari, Tal Mizrahi and Ken Gray
for their detailed review, comments and contributions.
A special thank you goes to David Ward and Tom Edsall for their
guidance and feedback.
Additionally the authors would like to thank Carlos Pignataro and
Larry Kreeger for their invaluable ideas and contributions which are
reflected throughout this draft.
Lastly, Reinaldo Penno deserves a particular thank you for his
architecture and implementation work that helped guide the protocol
concepts and design.
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16. IANA Considerations
16.1. NSH EtherType
An IEEE EtherType, 0x894F, has been allocated for NSH.
16.2. Network Service Header (NSH) Parameters
IANA is requested to create a new "Network Service Header (NSH)
Parameters" registry. The following sub-sections request new
registries within the "Network Service Header (NSH) Parameters "
registry.
16.2.1. NSH Base Header Reserved Bits
There are ten bits at the beginning of the NSH Base Header. New bits
are assigned via Standards Action [RFC5226].
Bits 0-1 - Version
Bit 2 - OAM (O bit)
Bits 2-9 - Reserved
16.2.2. MD Type Registry
IANA is requested to set up a registry of "MD Types". These are
8-bit values. MD Type values 0, 1, 2, 254, and 255 are specified in
this document. Registry entries are assigned by using the "IETF
Review" policy defined in RFC 5226 [RFC5226].
+---------+--------------+---------------+
| MD Type | Description | Reference |
+---------+--------------+---------------+
| 0 | Reserved | This document |
| | | |
| 1 | NSH | This document |
| | | |
| 2 | NSH | This document |
| | | |
| 3..253 | Unassigned | |
| | | |
| 254 | Experiment 1 | This document |
| | | |
| 255 | Experiment 2 | This document |
+---------+--------------+---------------+
Table 1
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16.2.3. TLV Class Registry
IANA is requested to set up a registry of "TLV Types". These are 16-
bit values. Registry entries are assigned by using the "IETF Review"
policy defined in RFC 5226 [RFC5226].
16.2.4. NSH Base Header Next Protocol
IANA is requested to set up a registry of "Next Protocol". These are
8-bit values. Next Protocol values 0, 1, 2 and 3 are defined in this
draft. New values are assigned via Standards Action [RFC5226].
+---------------+-------------+---------------+
| Next Protocol | Description | Reference |
+---------------+-------------+---------------+
| 0 | Reserved | This document |
| | | |
| 1 | IPv4 | This document |
| | | |
| 2 | IPv6 | This document |
| | | |
| 3 | Ethernet | This document |
| | | |
| 4..253 | Unassigned | |
+---------------+-------------+---------------+
Table 2
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17. References
17.1. Normative References
[RFC0791] Postel, J., "Internet Protocol", STD 5, RFC 791,
September 1981.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
17.2. Informative References
[RFC2784] Farinacci, D., Li, T., Hanks, S., Meyer, D., and P.
Traina, "Generic Routing Encapsulation (GRE)", RFC 2784,
March 2000.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC6071] Frankel, S. and S. Krishnan, "IP Security (IPsec) and
Internet Key Exchange (IKE) Document Roadmap", RFC 6071,
February 2011.
[SFC-PS] Quinn, P., Ed. and T. Nadeau, Ed., "Service Function
Chaining Problem Statement", 2014, <http://
datatracker.ietf.org/doc/
draft-ietf-sfc-problem-statement/>.
[SFC-arch]
Quinn, P., Ed. and J. Halpern, Ed., "Service Function
Chaining (SFC) Architecture", 2014,
<http://datatracker.ietf.org/doc/draft-quinn-sfc-arch>.
[VXLAN-gpe]
Quinn, P., Agarwal, P., Kreeger, L., Lewis, D., Maino, F.,
Yong, L., Xu, X., Elzur, U., and P. Garg, "Generic
Protocol Extension for VXLAN",
<https://datatracker.ietf.org/doc/draft-quinn-vxlan-gpe/>.
[dcalloc] Guichard, J., Smith, M., and S. Kumar, "Network Service
Header (NSH) Context Header Allocation (Data Center)",
2014, <https://datatracker.ietf.org/doc/
draft-guichard-sfc-nsh-dc-allocation/>.
[moballoc]
Napper, J. and S. Kumar, "NSH Context Header Allocation --
Mobility", 2014, <https://datatracker.ietf.org/doc/
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draft-napper-sfc-nsh-mobility-allocation/>.
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Authors' Addresses
Paul Quinn (editor)
Cisco Systems, Inc.
Email: paulq@cisco.com
Uri Elzur (editor)
Intel
Email: uri.elzur@intel.com
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